Vehicles used for the transport of passengers, or for commercial traffic such as the transport of heavy cargo loads, often contain so-called driving speed control units, also called cruise control units, for increasing travelling comfort and improving the utility of the vehicle. Such units control or maintain the vehicle's speed during operation without the requiring the vehicle operator to actuate an accelerator pedal or a brake pedal. Control is achieved by obtaining the current speed and the requested target speed of the vehicle, and by varying an input torque of the prime mover of the vehicle, or by controlling vehicle braking system, in order to achieve or maintain the target speed.
In some systems, the operation of the driving speed control unit is interrupted by the driver's actuation of the brake pedal or accelerator pedal. In this case, the automatic vehicle speed control is terminated, and the driver may then adjust or maintain the speed of the vehicle through operation of the brake and accelerator controls. The driver may later relinquish control to the driving speed control unit, such as by sending a “Resume Speed” command to the driving speed control unit through a button or other control input. In some systems, the driving speed control unit will then adjust the vehicle speed to a previous vehicle speed, such as the speed of the vehicle when the driving speed control unit was disabled. Such a previous speed may be stored in the memory of the driving speed control unit for this purpose. The rate of acceleration used to reach the previous vehicle speed is often a predetermined value selected by the driving speed control unit without consideration of various vehicle operating conditions. As a result, travelling comfort can be reduced, and the risk of damaging cargo transported by the vehicle increases.